Cytomegalovirus (CMV) is the leading infectious cause of birth defects which can result in deafness and mental retardation in neonates, and can cause severe viral pneumonia and colitis in transplant recipients and sight-threatening retinitis in patients with AIDS. Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with a number of cancers including Burkitt lymphoma, nasopharyngeal carcinoma, Hodgkin lymphoma, and post-transplant lymphoproliferative disease. Human CMV and EBV naturally infect humans, but not small animals or nonhuman primates. The best models currently available for CMV and EBV are rhesus monkey CMV and EBV. The goal of this study is to develop an effective vaccine for these rhesus viruses and to use these as a model for vaccines for their human counterparts. We are also studying which cellular proteins are important for infection of cells with HCMV and EBV. Last year we reported that the laboratory passaged strain of rhesus CMV, 68-1, which has been used in studies of pathogenesis and vaccine development, has insertions, deletions, and stop codons in several genes compared with the unpassaged isolate isolated directly from the monkey. Virus genes important for cellular tropism and for immune evasion were the most common sites of mutations in laboratory isolates of the virus. A vaccine is not available for prevention of EBV. The major target of antibodies to EBV is viral glycoprotein 350/220 (gp350) that mediates attachment to B cells through complement receptor 2 (CR2/CD21). A soluble gp350 vaccine has been tested in humans, and while it reduces the rate of infectious mononucleosis, it does not reduce the rate of EBV infection. This year, we created self-assembling nanoparticles that display different domains of gp350 in a symmetric array. By focusing presentation of the CR2-binding domain on nanoparticles, potent antibodies that neutralize EBV infection of B lymphocytes were elicited in mice and non-human primates. The nanoparticle vaccine increased neutralization 10- to 100-fold compared to soluble gp350 vaccine by targeting a functionally conserved site of vulnerability, improving vaccine-induced protection in a mouse model. This rational approach to EBV vaccine design elicited potent neutralizing antibody responses by arrayed presentation of a conserved viral entry domain, a strategy that can be applied to other viruses.